Marcello, come here! Hurry up...we have dinosaurs!

Italy is not exactly renown for dinosaurs. During their reign, between 230 and 66 million years ago, the ancient Mediterranean area was formed by countless small islands far from all major mainlands and thought to be unsuitable to sustain large animals like the dinosaurs. Or so we believed.
Published in Ecology & Evolution
Marcello, come here! Hurry up...we have dinosaurs!

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When I was a 5 years old Southern Italian intoxicated with dinosaur movies, pop art and toys, my parents tried to discourage me from following the dark path that eventually led me today to become a vertebrate palaeontologist. One of their main arguments used in trying to make an honest engineer or physician out of me was saying that our country wasn't exactly like North America, rich in fossil-bearing rocks, and that these extinct animals were likely never present in Italy. They weren't entirely wrong though! Their belief was based on the assumption, supported by the mainstream geological knowledge of the time, that most of the Mediterranean area was, at the time of the dinosaurs (between ~230 and 66 million years ago) represented by countless small islands far from all major mainlands – Europe, Africa, and Asia – and then unsuitable to sustain these prehistoric behemoths. During my childhood, the first, exciting remains of dinosaurs started to emerge here and there in the Italian territory, most remarkably the tiny Scipionyx, an extraordinarily preserved theropod dinosaur chick that made the cover of Nature in 1998. New isolated findings continued to emerge, and a vast record of footprints richly popped up to inspire a different story for prehistoric Italy. More connections with large continental areas maybe were seldom possible and could have potentially hosted isolated populations of these amazing animals of the past in one of these “proto-Italian” islands.

In 1994 a geology student, Tiziana Brazzatti, made an outstanding discovery of pivotal importance for this story. During a trip to a site nearby the city of Trieste, Northern Italy, she spotted some weird black shapes emerging from the pale limestones. Dinosaur bones! And not just a bunch of them, a whole skeleton of a duck-billed dinosaur was recovered from the site and nicknamed ‘Antonio’.

The author (AAC) in front of the holotype skeleton of Tethyshadros insularis, nicknamed Antonio, showing either scepticism for the interpretations on the palaeobiology of this taxon, or for his own bold fashion choice of the time (Picture © Giacomo Mengozzi; courtesy of Soprintendenza Archeologia, belle arti e paesaggio del Friuli-Venezia Giulia).

Fifteen years later, the palaeontologist Fabio Marco Dalla Vecchia christened the species Tethyshadros insularis using Antonio as the holotype (=namesake) of the species. This was not the usual duckbilled dinosaur, since its ~4 m of body length were easily dwarfed by many of its giant continental counterparts, which rivalled in size with Tyrannosaurus rex. For this reason, given the insular context that was attributed to the Villaggio del Pescatore area, the site where Tethyshadros was discovered, this Italian dinosaur was considered as a perfect example of the island rule. This ecological law describes the evolutionary miniaturisation of bigger animals in an insular environment due, for example, to the scarcity of resources and/or reduced competition pressures. Like the tiny, dog-sized Sicilian elephants of tens of million years later, the ancestors of these dinosaurs “island-hopped” from the nearby continental areas, settled on one of these islands of the “European archipelago”, and reduced their sizes as an evolutionary response due to pressure exerted by the scarcity of resources, richly available in vast areas compared to the small, island settings. But Antonio wasn’t the only keeper of this evolutionary mystery and wasn’t either alone at Villaggio del Pescatore.

In a new study published today, my co-authors and I describe the skeletons of some of the most beautiful and pristine dinosaurs from the site, and in particular of an almost complete one, belonging to an individual nicknamed ‘Bruno’.

Figure 2 of our new paper: Bruno (a), the second and bigger specimen of Tethyshadros: look how awesomely preserved its skull (b) is! You can even see its braincase in almost perfect anatomical connection (c). How cool is that?!

The skeleton of Bruno is bigger in size than the one of Antonio. By analysing the bone microstructure of both individuals, we found out that Antonio represents a younger individual of Tethyshadros, while Bruno is an older individual – which potentially could have still been growing at the time of its death.

Thin section under the microscope from a bone with the rock matrix surrounding the skeleton of Antonio. Analyses of fossilised bone sections help palaeontologists to derive important information on the growth stage of extinct dinosaurs at the time of their death. Also, they look pretty cool on Instagram.

Gathering geological evidence directly from the site where these skeletons come from, our team was also able to date with more precision the site and its fossils to approximately 80 million years ago, in the Cretaceous period. This is about 10 million years older than previously thought, quite a long time even when dealing with dinosaurs! At this time, what is now north-eastern Italy was a land facing a vast ocean but connected to western Europe and Asia, different from the small island that was previously considered for the Villaggio del Pescatore area. This means that not only small islands characterized the ancient Mediterranean, but many migratory routes from large terrestrial animals like the dinosaurs might have been possible across land bridges of what we nowadays call Italy. Investigating the phylogenetic relationships (the evolutionary relatedness of this species with closely related ones) of Tethyshadros insularis based on the new investigation of these specimens, allowed to strengthen this biogeographic interpretation, since the closer relatives of this dinosaur likely came from Asia around 90 million years ago. But that’s not all. Evolutionary trees have been of pivotal importance in biology since the first time Darwin sketched one in his notebook to represent his idea of inter-relationships between all living things. With the same tools, we can now trace the speed and spatial spread of a virus, with the emerging of new variants… But we can also reconstruct the tempo and mode in the evolution of a specific feature in a group of animals, like the rate of body-size evolution in the branch of duck-billed dinosaurs which includes our friends Bruno and Antonio.

Evolution of body size in Hadrosauriformes, the group including Tethyshadros insularis (red). No clear accelerated and directional trend in the reduction of body size is detected, meaning that this dinosaur likely belonged to a branch of the tree which ancestrally hadn’t yet developed the giant body-size of their later diverging relatives.

By doing so, my co-authors and I were able to test whether an accelerated, significant trend in body-size miniaturisation was occurring in the lineage of Tethyshadros. Short answer: not really! What we found out instead was that Tethyshadros is part of an earlier radiation compared to its more recent, giant relatives from North America and Asia, and that its body-size (even accounting for the possibility that Bruno, the most mature individual, might have still been growing at the time of its death) was more in line with its Asian, closely allied contemporaries. Several biogeographic models might explain the spread into Europe of an earlier radiation of hadrosauroids, preceding the emergence of the pre-extinction, bigger ones. Italy might have played a pivotal role in this palaeobiogeographic story, working as a continental bridge from Asia to Western Europe, Africa, and vice versa. We predict that with more fieldwork and research activity, we might be able to reveal a wider, potentially unexpected knowledge of earlier diverging hadrosauriforms than we currently envision.

The Villaggio del Pescatore site (star) falls on the coast of a “blank space in the map”, a potentially vast land representing a continental bridge and providing a suitable connection for Cretaceous dinosaurs to migrate across the prehistoric Italian territory. Map courtesy of Ron Blakey © 2020 Colorado Plateau Geosystems Inc.

This multidisciplinary effort sparks many interesting possibilities for Italian palaeontology: several migratory routes for large terrestrial animals like the dinosaurs might have been possible across land bridges of what we nowadays call Italy, and the treasure trove of Villaggio del Pescatore is evidence of that.

Villaggio del Pescatore, 80 million years ago. The first locality in Italy preserving many dinosaur individuals of the same species is here brought to life by scientific illustrator Davide Bonadonna. An adult and two juvenile individuals of the dinosaur Tethyshadros insularis showing the different appearances exhibited by immature and mature specimens of this dinosaur.

We do not want to just emphasise the “first” in terms of exceptional findings this research represents, but most importantly the pivotal role of the Italian dinosaur fossil record for evaluating interesting scientific hypotheses on these ancient animals and their ecosystems. As the site is already protected from the Italian institutions, new research and didactic activities may represent an opportunity to include the geological and paleontological heritage in the ‘must see’ list while visiting the “Belpaese”.
Come for the wine, stay for the dinosaurs.

The link to our open access paper in Scientific Reports is here.

This was an exciting team effort and a very fun and satisfying project to work on, in which a friendly group of collegues worked together to reveal the secret of this amazing palaeontological heritage. The researchers involved in the study are: Alfio Alessandro Chiarenza (Mapas Lab, University of Vigo), Matteo Fabbri (Field Museum of Natural History, Chicago), Lorenzo Consorti (University of Trieste and Geological Survey of Italy – ISPRA),  Juan Cantalapiedra (Universidad de Alcalá), David Evans (Royal Ontario Museum and University of Toronto), Federico Fanti and Marco Muscioni (University of Bologna).

Last and most importantly, thanks to the many institutions that allowed us to work on their specimens, in particular to the Soprintendenza Archeologia, Belle Arti e Paesaggio del Friuli-Venezia Giulia; Zoic s.r.l., Trieste; Museo Civico di Storia Naturale di Trieste; Comune di Trieste and the University of Trieste.

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